Sunday, February 7, 2010

Sample size- true or false?

when chosing the sample size for estimating a population proportion p to within E units with confidence (1-alpha)100%, if you take p=0.5 as the approximation to p, you will always obtain a sample size that is at least as large as required.





True or FalseSample size- true or false?
true.








If we don't know anything about phat and are still asked to find the sample size we let phat = 0.5. This maximizes the value of the error term and if n is sufficient for phat = 0.5, the n will be sufficient for all other values of phat.





this is easy to prove with a couple calculus steps.





find the the first and second derivate with respect to phat of


z * sqrt(phat * (1- phat) / n)





you'll find that the function is concave down and has a max when phat = 0.5Sample size- true or false?
On the whole, true.
True.
True.
true for sure, coz you cant mov ethe alpha-1

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